Research has been directed towards the purification of the hormone (IL-2) that specifically stimulates the growth of T cells. The objective of this work is to purify murine IL-2 to homogeneity and determine its amino acid sequence. A T cell tumor has been found that produces large amounts of IL-2, and this serves as the source of IL-2 for purification. The purification and sequence of IL-2 from human T cells will also be performed.